📚 node [[20210404104508 lisp_primitives]]

When implementing a Lisp in particular, the goal should be to express the totality of the Lisp with only a minimal set of implementation language code. For example, it wouldn't make a lot of sense to implement when in the source language (say, C) when, if if is implemented, it could be expressed as if1

Primitives include but are not limited to:

  • Basic data types

  • Any arithmetic

  • lambda or equivalent

    • if

  • cond

  • list

  • apply

  • defmacro

  • quote

The rest of a Lisp is simply library code, which can be expressed using all of the above.

Footnotes

1In fact, it could be expressed like this:

; a copy of emacs's own =when= definition
(defmacro my-when (condition &rest body)
  (list 'if condition (cons 'progn body)))

(macroexpand '(my-when t
         (message "hello world I did it")))
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